So recently been getting terrible gas mileage , full tank an only 50 miles an it’s already at half a tank! An I baby this car, highway at 55mph. Not a lead foot .
New plugs,
New air filter
New fuel filter
Runs good, no black smoke. Curious to know if it’s a 02 sensor ?
I had a cel come on not long ago but when I got home and turned the car off and tried to read the codes it don’t give me a cel light or anything at all! Dazed and confused .
Have you tried any fuel additives? Those three seem to main the main culprits. I’ve used “Gumout Regane” with decent results. But it sounds like you’re getting ~8 mi/gal which — well there’s something REALLY wrong.
What about your tire pressure? Or brake calipers sticking?
Are you feeling any loss of power?
My tire pressure is at 35lbs in every tire , I don’t feel any loss in power significantly . I did check to see if the brakes were stuck but I jacked up the car and rolled the 4 wheels and seen if there was any grinding . Nothing at all or anything holding them back. One thing I’ve noticed is when I’m driving I’ll smell rotten eggs like crazy. I know that means catalytic converter . But could that be causing this whole issue?
So update , I hollowed the catalytic converter (it was clogged very badly) , put a new 02 sensor. It runs good an no smoke but anytime I get about half tank or less it just starts dropping immediately. Is it quite possible the fuel sender unit isn’t working correctly at half tank or less ? Sorry to bother ya. Don’t mean to keep bringing up this thread. Just thought I’d ask the expert! Thank you.
The fuel tank is “oddly shaped” so after about half tank, it is normal to drop a little faster. I wouldn’t be concerned about that. What’s your current miles per gallon? The only way to really figure this out is to fill up with gasoline to auto-stop via the gas pump, reset trip meter, drive like 200mi or so, then fill up to auto-stop via the pump again, and divide your miles driven by the number of gallons just pumped. Don’t eyeball the fuel gauge 
I filled it up all the way to a full tank an just ran out of gas at 217 miles . It is a automatic but just dont sound right, my old gen 2 got 300 np at all even with 230k haha. An i didnt rely on the guage cause i figured it was probably not correct after 30+ years lol.
Did you try checking your fuel filter? When you run your engine, make sure there’s no fuel leaking from the fuel rail. I found a leak and replaced ALL my O-rings for my fuel injectors.
Nah that doesn’t sound right at all even if all city driving with AC blasting. Mixed driving you should be getting close to 300mi a tank.
Did you reset your ECU after replaced everything? What brand O2 sensor did you install?
I did replace the fuel filter as well. It was pretty rough but since than still hasnt been getting good mpg. An their is no fuel leaks haha. Checked my fuel rail cant visually see anything nor smell anything.
The 02 sensor i had used was a denso 02 sensor. I know i shouldve went oem but its just so expensive for one. An yeah been trying to chase this problem down. If this helps i get code 12 which is for egr solenoid i believe. Could that be the problem? Wouldnt think it would affect it so severly . An yes i did reset the ecu. Pulled all the fuses as well. To ensure it did reset.
Nah I used Denso too and would recommend it. I’m also getting a EGR 12 but my mileage is fine. Is the car running rough at all ? What’s the warmed up idle RPM?
If your engine is not revving at a high RPM and you don’t feel a drag on your car, it shouldn’t be consuming more fuel.
Did you confirm your tank is really only half tank after running it and not a bad fuel sensor?
The car is not running rough at all which i thought at first it was running really rich but it isnt . No misfires or nothing. An the warm idle is around 800rpm . Which is normal. So idk i dont see any fuel leaking or smelling it . While driving.
The sensor is out , which i figured on a 30 year old car, what ive done is filled it up all the way to the brim , drive the car until it literally runs out of gas . Which is only 217 miles ive gotten on a full tank. I did verify to check if the tank was really full an it was indeed. Could the fuel sensor be causing the computer to think its out of fuel ? An no leaks at all which is quite weird. Could it quite possibly be a clogged return line?
Just curious, are you running on 87 or 91 octane, and does it have ethanol in the gas?
I noticed that when I was using gas w/ 10% ethanol, I had really crappy gas mileage. I had to find a station that was ethanol-free.
It shouldn’t be THAT noticeable of a difference though. This one really has me stumped. If it was leaky fuel injectors I believe you’d notice a really rough idle.
Can you try a shot of that Gumout Regane to see if that helps?